JP2012150434A - Image forming apparatus and control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique to suppress rotational drive of a conveyance body merely for a purpose of obtaining a light quantity of reflected light received by an optical sensor.SOLUTION: A printer 1 comprises: a belt 13; a mark sensor 15; a driving mechanism 47 for executing detection rotation for rotatively driving the belt 13 for detecting a mark and non-detection rotation for rotatively driving the belt 13 for a purpose other than the detection of a mark; a CPU 40 for obtaining a quantity of light received on the mark sensor 15 in the non-detection rotation for determining an adjustment value for sensor sensitivity on the basis of the quantity of the received light; and the CPU 40 for detecting the mark with the sensor sensitivity having been adjusted with the determined adjustment value in the detection rotation.

Description

  The present invention relates to a technique for irradiating light to a rotationally driven carrier and obtaining a received light amount of reflected light from the irradiation area.

  Some image forming apparatuses have a function of correcting a shift of an image forming position on a sheet, for example. Specifically, in this image forming apparatus, a pattern composed of a plurality of marks such as a registration pattern is formed on the belt, and the reflected light is received while the belt is irradiated with light by an optical sensor. Based on the amount of reflected light received by the optical sensor, the difference in reflectance or amount of reflected light between the belt surface and the mark surface is read to determine the mark position, and image formation is performed based on the determination result. Misalignment is corrected.

  Here, for example, the surface of the belt may be scratched or dirty, and light is irregularly reflected by the scratch or dirt, so that the reflectivity of the belt surface is lowered and the mark determination may not be performed normally. Therefore, conventionally, there is a technique in which light is irradiated onto the surface of a belt on which no mark is formed by an optical sensor, and the light receiving sensitivity of the optical sensor is adjusted according to the amount of light received by the reflected light (see Patent Document 1).

JP 2008-134333 A

  However, if the degree of adhesion of scratches or dirt varies depending on the position of the belt surface, the reflectance of the belt surface also varies depending on the position, and the amount of reflected light received by the optical sensor varies accordingly. However, the above conventional configuration is a configuration in which the light receiving sensitivity is adjusted according to the amount of light received in a single point at a certain point in the optical sensor without considering such variation in reflectance. . For this reason, even if the light receiving sensitivity of the optical sensor is adjusted, there is a problem in that the measurement accuracy of the mark varies depending on the amount of light received by the single reflected light.

  Thus, a configuration is conceivable in which the belt is driven to rotate and the light receiving sensitivity of the optical sensor is adjusted according to the amount of reflected light received at different time points. However, it is not preferable to rotationally drive the belt only to acquire the amount of reflected light received because it wastes time and the life of the apparatus.

  The present specification discloses a technique for suppressing rotationally driving a carrier such as the belt just to acquire the amount of reflected light received by the optical sensor.

An image forming apparatus disclosed in the present specification includes a rotation driven conveyance body, a light projecting unit that irradiates light on the conveyance body, and a light receiving unit that receives reflected light from the conveyance body. When printing on the image forming medium with the sensor, a print image is formed on the transport body or on the image forming medium transported to the transport body, and when the mark is detected by the optical sensor, the correction mark is transferred to the transport body. An image forming unit formed on an image forming medium conveyed on the body or on the conveying body, a detection rotation for rotating the conveying body to detect the mark, and the conveying body other than the detection of the mark A non-detection rotation for driving the rotation of the optical sensor, and a received light amount of the reflected light received by the optical sensor during the non-detection rotation, and adjusting the sensor sensitivity of the optical sensor from the received light amount Determine value A determination unit that, during rotation for the detection, and a mark detecting unit for detecting the mark sensor sensitivity after adjustment by the adjustment value determined by the determination unit.

  In the image forming apparatus, the transport body is a medium transport body that transports the image forming medium at the time of printing, the non-detection rotation is a rotational drive for the printing, and the determination unit includes the determination unit A configuration may be used in which a conveyance area utilization process is performed in which the adjustment value is determined using a received light amount of reflected light from a conveyance area that has conveyed the image forming medium in the medium conveyance body.

  In the image forming apparatus, the determination unit has a length of the image forming medium in the transport direction of the transport body equal to or greater than a reference length, and a width of the image forming medium in a direction orthogonal to the transport direction. The configuration may be such that if at least one of the conditions that the width is equal to or greater than the reference width is satisfied, the transfer area use process is executed, and if the condition is not satisfied, the transfer area use process is not executed.

  In the image forming apparatus, in the transport area use process, the weight for the light reception amount of the reflected light from the transport area is set larger than the weight for the light reception amount of the reflected light from the non-transport area that is not the transport area. The configuration may be a process for determining the adjustment value based on both received light amounts.

  In the image forming apparatus, the transport area utilization process may be a process of determining the adjustment value only from the amount of reflected light received from the transport area.

  In the image forming apparatus, the non-detection rotation is rotation driving for the printing, the image forming unit includes a plurality of image forming units that form images of different colors, and the determining unit is If the number of image forming units used at the time of printing is equal to or greater than the prescribed number, the amount of reflected light received by the optical sensor at the time of printing is not used for determining the adjustment value, and the image forming unit used at the time of printing is When the number is less than the specified number, the received light amount of the reflected light received by the optical sensor at the time of printing may be used to determine the adjustment value.

  In the image forming apparatus, the determination unit is configured to acquire a received light amount of reflected light received by the optical sensor a plurality of times or for a reference time, and the determination unit performs the plurality of times or the time during the non-detection rotation. In the case where all the received light amounts for the reference time cannot be acquired, the driving unit rotationally drives the carrier for adjusting the sensor sensitivity, and the determining unit acquires the remaining received light amount But you can.

  In the image forming apparatus, a determination unit that acquires a received light amount of reflected light received by the optical sensor during the non-detection rotation and determines at least one of a contamination degree of the optical sensor and a deterioration degree of the conveyance body. Prepare.

  The present invention is realized in various modes such as a control device, a control method, a printing device, a printing method, a computer program for realizing the functions of these methods or devices, and a recording medium on which the computer program is recorded. Can do.

  According to the present invention, it is possible to suppress the rotational driving of the carrier only for obtaining the amount of reflected light received by the optical sensor.

1 is a side sectional view showing a schematic configuration of a printer according to an embodiment of the present invention. Block diagram schematically showing the electrical configuration of the printer Perspective view of mark sensor and belt Diagram showing circuit configuration of mark sensor Flow chart showing printing process Flow chart showing sensitivity adjustment processing Schematic diagram of belt unit etc. showing the state where the non-transport area passes through the detection area Schematic diagram of belt unit etc. showing a state where the transport area passes through the detection area Flow chart showing correction processing

An embodiment will be described with reference to the drawings.
(Entire printer configuration)
FIG. 1 is a side sectional view showing a schematic configuration of a printer 1 (an example of an image forming apparatus) according to the present embodiment. The printer 1 is a multi-transfer tandem color printer that forms a color image using, for example, four color toners of black K, yellow Y, magenta M, and cyan C.

  1 is the front side of the printer 1 (indicated by an arrow F in each figure), and the depth direction of the paper is the left-right direction of the printer 1. In the following description, when each component or term of the printer 1 is distinguished for each color, K (black), C (cyan), M (magenta) means each color at the end of the code of the component. ), Y (yellow).

  The printer 1 includes a casing 2, and a tray 4 on which a plurality of sheets 3 (specifically, examples of image forming media such as paper and OHP sheets) can be stacked at the bottom of the casing 2. ing. A pickup roller 5 is provided above the front end of the tray 4, and this pickup roller 5 is rotationally driven to send out the sheet 3 stacked on the top of the tray 4 to the registration roller 6. The registration roller 6 corrects the skew of the sheet 3 and then conveys the sheet 3 onto the belt unit 11.

  The belt unit 11 has a configuration in which an annular belt 13 (an example of a conveyance body and a medium conveyance body) is stretched between a pair of support rollers 12A and 12B. The belt 13 is made of a resin material such as polycarbonate, and the surface thereof is mirror-finished. The belt 13 circulates and moves in the clockwise direction on the paper surface when the rear support roller 12B is driven to rotate, and conveys the sheet 3 placed on the upper surface thereof to the rear. Four transfer rollers 14 are provided inside the belt 13, and each transfer roller 14 is opposed to a photosensitive member 28 of each of the process units 19 </ b> K to 19 </ b> C described later with the belt 13 interposed therebetween.

  A mark sensor 15 (an example of an optical sensor) for detecting the position of a mark M (see FIG. 3) formed on the surface of the belt 13 when a correction process described later is executed is performed on the rear end side of the belt 13. Is provided. Further, a cleaning device 16 that collects toner (including a correction pattern P described later), paper dust, and the like attached to the surface of the belt 13 is provided below the belt unit 11.

  Above the belt unit 11, four exposure units 17K, 17Y, 17M, and 17C and four process units 19K, 19Y, 19M, and 19C are provided side by side in the front-rear direction. A set of image forming units 20 (an example of an image forming unit) is configured to include each of the exposure units 17K to 17C, the process units 19K to 19C, and the transfer roller 14 described above. Four sets of image forming units 20K, 20Y, 20M, and 20C corresponding to the respective colors of black, yellow, magenta, and cyan are provided.

  Each exposure unit 17 </ b> K to 17 </ b> C includes an LED head 18, and a plurality of LEDs (not shown) are arranged in a line in the left-right direction of the printer 1. Each of the exposure units 17K to 17C is controlled to emit light based on image data to be formed, and performs exposure by irradiating light from the LED head 18 to the surface of the opposing photoconductor 28 line by line.

  In the present embodiment, the alignment direction of the plurality of LEDs of each exposure unit 17 (the depth direction in FIG. 1) is the main scanning direction. Also, the direction perpendicular to the main scanning direction, and the arrangement direction of the four process units 19K, 19Y, 19M, and 19C, in other words, the four photosensitive members 28 is the sub-scanning direction.

  Each of the process units 19K to 19C includes a toner storage chamber 23 that stores toner of each color that is a colorant. The toner in the toner storage chamber 23 is supplied onto the supply roller 24, and the toner on the supply roller 24 is positively frictionally charged with the development roller 25 while being supplied to the development roller 25. The toner on the developing roller 25 is further frictionally charged with the layer thickness regulating blade 26 to be a thin layer having a constant thickness.

  Each of the process units 19K to 19C includes a photoreceptor 28 whose surface is covered with a positively chargeable photosensitive layer, and a scorotron charger 29. At the time of mark detection and printing, the photosensitive member 28 is rotationally driven, and accordingly, the surface of the photosensitive member 28 is uniformly positively charged by the charger 29. The positively charged portion is exposed by the exposure units 17K to 17C, and an electrostatic latent image is formed on the surface of the photoreceptor 28.

  Next, the toner on the developing roller 25 is supplied to the electrostatic latent image, whereby the electrostatic latent image is visualized to form a toner image. Thereafter, the toner image carried on the surface of each photoconductor 28 is negatively applied to the transfer roller 14 while the sheet 3 passes through each transfer position between the photoconductor 28 and the transfer roller 14. The images are sequentially transferred onto the sheet 3 by the transfer voltage. The sheet 3 on which the toner image has been transferred is then conveyed to the fixing device 31 where the toner image is thermally fixed, and then the sheet 3 is conveyed upward and discharged onto the upper surface of the casing 2.

(Electrical configuration of printer)
FIG. 2 is a block diagram schematically showing the electrical configuration of the printer 1. The printer 1 includes a CPU 40 (an example of a determination unit, a mark detection unit, and a determination unit), a ROM 41, a RAM 42, an NVRAM 43 (nonvolatile memory), and a network interface 44 as shown in FIG. The units 20K to 20C, the mark sensor 15, the display unit 45, the operation unit 46, and a drive mechanism 47 (an example of a drive unit) are connected.

  The ROM 41 stores a program for executing various operations of the printer 1 such as a printing process described later. The CPU 40 stores the processing result in the RAM 42 or the NVRAM 43 according to the program read from the ROM 41. Control each part. The network interface 44 is connected to an external computer (not shown) or the like via a communication line, thereby enabling mutual data communication.

  The display unit 45 includes a liquid crystal display, a lamp, and the like, and can display various setting screens and operation states of the apparatus. The operation unit 46 includes a plurality of buttons, and various input operations can be performed by the user. The drive mechanism 47 includes a drive motor and the like, and rotationally drives the belt 13 and the like.

(Configuration of mark sensor)
As shown in FIG. 3, one or a plurality of mark sensors 15 (for example, two in this embodiment) are provided on the lower rear side of the belt 13, and these two mark sensors 15 are arranged side by side in the left-right direction. ing. Each mark sensor 15 is a reflective optical sensor including a light emitting element 51 (for example, an example of an LED light projecting unit) and a light receiving element 52 (for example, an example of a phototransistor light receiving unit). Specifically, the light emitting element 51 irradiates light on the surface of the belt 13 from an oblique direction, and the light receiving element 52 receives reflected light from the surface of the belt 13. A spot area formed on the belt 13 by light from the light emitting element 51 is a detection area E of the mark sensor 15.

  FIG. 4 is a circuit diagram of the mark sensor 15. The received light signal SA from the light receiving element 51 becomes lower as the received light amount level of the reflected light received by the light receiving element 52 becomes higher, and becomes higher as the received light level becomes lower. The light reception signal SA is input to the hysteresis comparator 53. The hysteresis comparator 53 compares the received light signal SA level with threshold values (first threshold value TH1, second threshold value TH2), and outputs a binarized signal S2 whose level is inverted according to the comparison result. Note that the CPU 40 can acquire not only the binarized signal S2 but also the digital signal SC obtained by A / D converting the received light signal SA by the A / D converter 54.

(Printing process)
FIG. 5 is a flowchart showing the printing process. For example, when the CPU 40 receives print data from an external computer via the network interface 44 or a print command is input from the operation unit 46, the CPU 40 executes print processing shown in FIG. In the course of this printing process, an adjustment value for the sensor sensitivity of the mark sensor 15 is determined.

  First, the CPU 40 activates the drive mechanism 47 to rotationally drive the belt 13 (S1). As a result, the belt 13 starts rotational driving for printing (an example of non-detection rotation). Next, the CPU 40 determines whether or not printing to be executed at present is monochrome printing (S2). Here, normally, the black toner K is used more frequently than the other color toners Y, M, and C, and therefore the black toner K disappears from the toner storage chamber 23 before the quality of the toner itself deteriorates and becomes unsuitable for printing. There are many. On the other hand, the other color toners Y, M, and C are less frequently used than the black toner K, and thus the quality of the toner itself is deteriorated even though the toner remains in the toner storage chamber 23, and is not suitable for printing. There is a case that becomes a state. Such deterioration of the toner is mainly caused by the operation amount of the process unit 19. That is, as the operation amount of the process unit 19 increases, stress is applied to the toner stored in the toner storage chamber 23, and damage is accumulated in the toner. If the quality of the toner itself deteriorates, the charging performance of the toner becomes unstable, and proper development and transfer cannot be performed, and the toner may adhere to an unintended place. Therefore, the other color toners Y, M, and C are more likely to be scattered on the belt 13 than the black toner K, or remain uncleaned from the belt 13. Since the amount of reflected light received by the mark sensor 15 varies at the time of sensitivity adjustment on the surface of the belt 13 thus soiled, the accuracy of sensitivity adjustment may be reduced.

  Therefore, when the printing to be executed at present is color printing (S2: NO), the other color toners Y, M, and C are used. Therefore, the CPU 40 does not perform the sensitivity adjustment process and does not execute the sensitivity adjustment process. Printing for forming a print image based on the print data or the like on the sheet 2 is executed (S8), and this print processing is terminated.

  On the other hand, when the printing to be executed at present is monochrome printing (S2: YES), the CPU 40 has a total length in the conveyance direction of the sheet 3 to be printed (hereinafter simply referred to as the total length of the sheet 3) equal to or greater than the reference length. Whether or not (S3). When there are a plurality of printed sheets, the total length of the sheet 3 is a total value of the lengths of the sheets 3 corresponding to the number of printed sheets. The reference length is a length corresponding to the amount of movement of the belt 13 when the digital signal SC from the mark sensor 15 is sampled by an amount necessary for fine adjustment of sensitivity adjustment processing described later.

  In the present embodiment, in fine adjustment, the digital signal SC needs to be sampled 30 times at predetermined time intervals. Here, for example, if the sheet 3 to be printed is a standard A4 size, the reference length is the total value of the lengths of the three sheets 3. If the sheet 3 to be printed is a standard B5 size, the reference length is the total value of the lengths of the five sheets 3. Thus, the reference length is the total value of the number of sheets corresponding to the size of the sheet 3 to be printed, and is preferably equal to or greater than the entire circumference of the belt 13. By using the digital signal SC from the mark sensor 15 acquired over the entire circumference of the belt 13, it is possible to prevent the sensor sensitivity from being adjusted accurately due to variations in the reflectance of the surface of the belt 13. is there. Hereinafter, the case where the size of the sheet 3 is the regular A4 size will be described as an example.

  When the total length of the sheet 3 is less than the reference length and the elapsed time from the previous sensitivity adjustment is less than the reference time (S3: NO and S4: NO), the sensitivity adjustment process is not executed. Only printing based on the print data or the like is executed (S9), and the printing process is terminated. The CPU 40 counts the elapsed time based on the internal clock, and the reference time is stored in advance in the NVRAM 43, for example.

  On the other hand, when the total length of the sheet 3 is greater than or equal to the reference length, in other words, when the number of sheets 3 to be printed is three or more (S3: YES), the CPU 40 is orthogonal to the conveyance direction of the sheet 3 to be printed. It is determined whether or not the width in the direction (hereinafter simply referred to as the width of the sheet 3) is equal to or greater than the reference width (S5). The reference width is substantially equal to the width passing through the detection area E of both the left and right mark sensors 15. If the width of the sheet 3 is equal to or larger than the reference width (S5: YES), a printing / sensitivity adjustment process is executed (S6). In this case, in printing to be executed at present, the belt 13 covers an area that is longer than the reference length and more than the reference width by the sheet 3 to be printed. In other words, the size of the transport area 13A (see FIG. 3) used for transporting the sheet 3 in the printing to be executed at present is not less than the reference length and not less than the reference width.

  However, even if the total length of the sheet 3 is less than the reference length (S3: NO), if the elapsed time from the previous sensitivity adjustment exceeds the reference time (S4: YES), it is highly necessary to adjust the sensitivity. Therefore, on the condition that the width of the sheet 3 is equal to or larger than the reference width (S5: YES), the printing / sensitivity adjustment process is executed (S6). In this case, in the printing to be executed at present, the size of the transport area is less than the reference length and more than the reference width.

  For example, when the width of the sheet 3 is less than the reference width (S5: NO), for example, when the sheet 3 to be printed is a postcard size (S5: NO), the non-transport area 13B that is not used for transporting the sheet 3 during printing is It passes through the detection area E. Since the sheet 3 is not on the non-transport area 13B and is exposed while passing directly under the image forming unit 20, the toner is more likely to adhere compared to the transport area 13A. Since the amount of reflected light received by the mark sensor 15 varies at the time of sensitivity adjustment on the surface of the belt 13 thus soiled, the accuracy of sensitivity adjustment may be reduced. Therefore, in this case, the CPU 40 executes only printing based on the print data or the like without executing the sensitivity adjustment processing (S8), and ends the printing processing.

  FIG. 6 is a flowchart showing the sensitivity adjustment processing, FIG. 7 is a schematic diagram of the belt unit 11 and the like showing a state where the non-transport area 13B passes the detection area E, and FIG. 8 shows the detection area E in the transport area 13A. It is a schematic diagram of belt unit 11 etc. which show the state which passes.

  When the width of the sheet 3 is equal to or larger than the reference width (S5: YES), the CPU 40 executes printing based on the print data and the like, and also executes sensitivity adjustment processing shown in FIG. First, the CPU 40 determines whether or not the belt 13 is rotating (S11). If the belt 13 is rotating (S11: YES), the sensor sensitivity is roughly adjusted (S12). Coarse adjustment is processing for determining an adjustment value of sensor sensitivity with a relatively low accuracy (an example of determination processing). At this time, the CPU 40 functions as a determination unit.

Specifically, the coarse adjustment has fewer sampling times of the digital signal SC than the fine adjustment described later. For example, the CPU 40 samples the digital signal SC ten times every unit time (for example, 0.3 seconds) in a state where the belt 13 is rotationally driven. In addition, the sampling of the digital signal SC in the coarse adjustment is performed when the non-transport area 13B passes through the detection area E as shown in FIG.

  Then, the CPU 40 determines the sensor sensitivity adjustment value based on the digital signal SC for 10 times so that the received light amount based on the digital signal SC becomes a predetermined level. This adjustment value may be any of the light projection amount of the light emitting element 51, the amplification degree of the light reception signal SA from the light receiving element 52, and the offset amount. The CPU 40 can adjust the sensor sensitivity of the mark sensor 15 by changing at least one of the light projection amount of the light emitting element 51, the amplification degree of the light reception signal SA from the light receiving element 52, and the offset amount. The CPU 40 adjusts the sensor sensitivity based on this adjustment value, and waits until the transport area 13A arrives at the detection area E (S13: NO). This arrival timing can be grasped from, for example, the time count from the feeding timing by the registration roller 6, the detection timing of the leading edge of the sheet 3 near the fixing device 31, and the like.

  As shown in FIG. 8, when the transport area 13A arrives at the detection area E (S13: YES), fine adjustment of the sensor sensitivity is started (an example of S14 transport area utilization processing). The fine adjustment is a process for determining the adjustment value of the sensor sensitivity with higher accuracy than the coarse adjustment. Specifically, the fine adjustment has more sampling times of the digital signal SC than the coarse adjustment. For example, the CPU 40 samples the digital signal SC 30 times every unit time (for example, 0.3 seconds) while the belt 13 is rotationally driven. Next, the CPU 40 determines whether or not the belt 13 stops before the completion of sampling of the digital signal SC for fine adjustment (S15).

  For example, when the total length of the sheet 3 to be printed is equal to or greater than the reference length and the width of the sheet 3 is equal to or greater than the reference width (S3: YES and S5: YES), the size of the transport area 13A is equal to or greater than the reference length. Before the belt 13 stops due to the end of printing, sampling of the digital signal SC for fine adjustment is completed (S15: NO). The CPU 40 determines an adjustment value of the sensor sensitivity based on the sampled digital signal SC 30 times so that the received light amount based on the digital signal SC becomes a predetermined level, and stores it in the NVRAM 43, for example.

  For example, if the total length of the sheet 3 to be printed is less than the reference length (S3: NO), but the width of the sheet 3 is greater than or equal to the reference width (S5: YES), the size of the transport area 13A is less than the reference length. Therefore, there is a possibility that the belt 13 stops due to the end of printing before the sampling of the digital signal SC is completed (S15: YES). In this case, in order to continue sampling of the digital signal SC for fine adjustment, the rotational driving of the belt 13 is continued (S16), and when the sampling of the digital signal SC for all 30 times is successful (S17: YES) ), Stop the belt 13 and proceed to S18.

  In this case, all 30 digital signals SC include those based on the amount of reflected light received from the transport area 13A and those based on the amount of reflected light received from the non-transport area 13B. The former is less affected by deposits (toner etc.) on the belt 13 than the latter. Therefore, the CPU 40 determines the adjustment value using the former and the latter after making the weight for the former larger than the weight for the latter (S18). More specifically, for example, an example of calculating a weighted average using the former and the latter can be considered. At this time, a weighted average is calculated using a coefficient for the former and a coefficient larger than that for the latter. Then, an adjustment value is determined based on the weighted average. For example, the former may be 1 to 2 with respect to 1, the latter may be 1 with respect to 0, and the like. That is, when the coefficient for the latter is 1 and the coefficient for the former is 4, the weighted average is calculated by the formula (4 × the former + 1 × the latter) / (4 + 1).

  For example, if the sampling fails because the digital signal SC becomes an abnormal level due to noise or the like (S17: NO), the adjustment value cannot be determined if the number of failures is equal to or greater than the reference number (S19: NO). A notification process such as displaying an error to the effect on the display unit 45 is performed (S22), the belt 13 is stopped, and the sensitivity adjustment process is terminated.

  If the number of failures is less than the reference number (S19: YES), if the elapsed time from the previous sensitivity adjustment is less than the reference time (S20: NO), the belt 13 is also stopped without determining the adjustment value. Then, the sensitivity adjustment process is terminated. On the other hand, if the elapsed time exceeds the reference time (S20: YES), it is highly necessary to adjust the sensor sensitivity, so sampling is performed again (S21), and the process proceeds to S17.

  When the sensitivity adjustment processing ends, the CPU 40 determines the degree of contamination (the degree of toner adhesion) of at least one of the light emitting element 51 and the light receiving element 52 and the degree of deterioration of the belt 13 from the amount of received light based on the sampled digital signal SC. The result is displayed on the display unit 45 (S7), and the printing process is terminated. Thereby, it is possible to suppress the rotational driving of the belt 13 only to determine the degree of contamination of the mark sensor 15 and the degree of deterioration of the belt 13. At this time, the CPU 40 functions as a determination unit.

(Correction process)
FIG. 9 is a flowchart showing the correction process. When the CPU 40 satisfies a predetermined condition, for example, when the image forming unit 20 or the belt unit 11 is replaced, a predetermined time elapses from the previous execution of the correction process, or the number of sheets of the image-formed sheet 3 reaches a predetermined number. 9 is executed.

  Since the CPU 40 has already determined the adjustment value of the sensor sensitivity in the printing process, the belt 13 is not rotationally driven only for sampling the digital signal SC based on the reflected light from the surface of the belt 13 in the correction process. The CPU 40 reads the determined adjustment value from the NVRAM 43 (S31), sets the sensor sensitivity, activates the drive mechanism 47, and rotationally drives the belt 13 (an example of S32 detection rotation).

  Next, as shown in FIG. 3, a correction pattern P composed of each color mark M is formed on the belt 13 (S33), and a binarized signal SB is acquired (S34). Then, the mark M is detected based on the binarized signal SB (an example of mark detection processing). At this time, the CPU 40 functions as a mark detection unit. The CPU 40 calculates a correction value for correcting the image misregistration between the colors from the detection result of the mark M (S35), stores it in the NVRAM 43, and ends this correction processing. The correction pattern may be composed of density correction marks.

(Effect of this embodiment)
(1) According to the present embodiment, the amount of reflected light received by the mark sensor 15 is acquired for sensor sensitivity adjustment during non-detection rotation in which the belt 13 is rotationally driven for purposes other than detection of the mark M. . As a result, it is possible to prevent the belt 13 from being rotationally driven only to acquire the amount of reflected light received by the mark sensor 15.

  (2) In the transport area 13A, compared to the non-transport area 13B, toner, dust, and the like are less likely to adhere to the surface due to the presence of the sheet 3 when the print image is formed by the image forming unit 20. Therefore, according to the present embodiment, the adjustment value is determined using the amount of reflected light received from the transfer area 13A. As a result, compared to the configuration in which the adjustment value is determined using only the amount of reflected light from the non-transport area 13B, a larger amount of received light that is less affected by the colorant or the like is acquired, and the sensor sensitivity adjustment accuracy is improved. Can be made. In particular, in the electrophotographic image forming apparatus, toner adheres to the photoconductor 28 more than necessary due to scratches on the photoconductor 28 and easily adheres to the belt 13. Therefore, it is particularly effective to use the transport area 13A. Is.

  (3) According to the present embodiment, only when the total length of the sheet 3 is equal to or greater than the reference length and at least one of the conditions that the width of the sheet 3 is equal to or greater than the reference width is satisfied, the conveyance area use process Execute. Thus, regardless of the length and width of the sheet 3, it is possible to efficiently acquire a received light amount that is less affected by toner or the like and to adjust the sensor sensitivity with high accuracy compared to the configuration in which the conveyance area utilization processing is executed. .

  (4) According to the present embodiment, the weight for the light reception amount of the reflected light from the transport area 13 is set larger than the weight for the light reception amount of the reflected light from the non-transport area 13B. Determine (S3: NO and S5: YES). That is, the adjustment value is determined by placing importance on the former amount of received light rather than the latter amount of received light. As a result, the influence of the toner or the like can be suppressed compared to a configuration in which the former amount of received light is not more important than the latter amount of received light.

  (5) According to the present embodiment, in the transport area use process, the sensor sensitivity adjustment value is determined only from the amount of reflected light received from the transport area 13A (S3: YES and S5: YES in FIG. 5). . Thereby, compared with the structure which determines an adjustment value also using the light reception amount of the reflected light from the non-transport area 13B, the influence by a toner etc. can be suppressed.

  (6) According to the present embodiment, when sampling is not completed during printing (S15 in FIG. 6: YES), the belt 13 is rotationally driven to adjust the sensor sensitivity, and the remaining received light amount is calculated. get. Thereby, even when the sampling is not completed during printing, the adjustment value can be determined by effectively using the already received light amount.

  It can be determined as follows whether a certain image forming apparatus performs a part or all of the above-described correction processing of the present embodiment. When the image forming apparatus has a memory and stores the adjustment value of the sensor sensitivity of the optical sensor in the memory, the adjustment value stored in the memory before and after execution of non-detection rotation, for example, printing If is changed, it can be determined that at least a part of the correction processing is performed.

  At this time, if the amount of reflected light received by the optical sensor is forcibly changed by changing the reflectance of the surface of the belt 13 before and after the non-detection rotation, the adjustment value before and after the execution of printing is changed. Since the change becomes remarkable, it can be judged more easily. Further, instead of the adjustment value, the adjustment target may be determined by detecting a change before and after execution of the non-detection rotation. For example, the received light amount received by the optical sensor with respect to the same amount of reflected light, in other words, the change in the amplification degree or the offset amount based on the change in the received light signal level may be detected and judged. Further, it may be determined by detecting a change in the amount of emitted light.

(Reference example)
In connection with the present invention, the following configuration can also be adopted.
“When performing functions that require rotational drive of the carrier, such as during printing, cleaning, or when performing belt slack suppression functions, the amount of reflected light received by the optical sensor is acquired, and contamination of the optical sensor is determined from the amount of received light. A configuration that determines at least one of the degree and the degree of deterioration of the conveyance body. "
For example, in the printing process, the contamination / deterioration determination (S7) is executed based on the sampled light reception signal SA without determining the adjustment value of the sensor sensitivity. According to this, it is possible to prevent the belt 13 from being rotationally driven only for acquiring the amount of received light for determining contamination / deterioration.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and the drawings, and for example, the following various aspects are also included in the technical scope of the present invention.
(1) In the above embodiment, the multiple transfer tandem printer is taken as an example, but the image forming apparatus of the present invention is not limited to this. A multi-transfer type transfer body type or a multiple development type (multi-rotation type, single-pass type) printer may be used. In this case, the photoconductor conveys an electrostatic latent image and a toner image. The developing device and the charger are examples of the image forming unit.

  In addition, a printer of a multiple transfer / intermediate transfer method (intermediate transfer member method / tandem method) may be used. In this case, the intermediate transfer member or the photosensitive member conveys an electrostatic latent image and a toner image. The developing device and the charger are examples of the image forming unit. Further, other electrophotographic printers such as a polygon scanning method may be used, and an ink jet printer may be used.

  (2) In the above embodiment, the adjustment value of the sensor sensitivity is determined when the belt 13 is rotated for printing. However, the non-detection rotation of the present invention is not limited to this. For example, some image forming apparatuses have a function of suppressing the slackness of the belt 13 by being rotationally driven when the belt 13 is continuously stopped for a predetermined time. In such an image forming apparatus, the sensitivity adjustment process shown in FIG. 6 may be executed while the belt 13 for the same function is rotating. Further, the sensitivity adjustment process shown in FIG. 6 may be executed while the belt 13 is driven to rotate for cleaning the belt 13 by the cleaning device 16.

  (3) In the above embodiment, the sensitivity adjustment processing is performed under the condition of monochrome printing, but the present invention is not limited to this. It may be configured to adjust the sensitivity for color printing. Further, the sensitivity adjustment process may be executed only when the number of image forming units 20 used for printing is less than a prescribed number (for example, two). As a result, even when the number of image forming units used at the time of printing is more than the specified number, it is less likely that the colorant will adhere to the carrier compared to the configuration in which the amount of light received by the optical sensor is acquired. The influence can be suppressed.

  (4) In the above embodiment, the digital signal SC for a plurality of times is sampled in order to determine the adjustment value of the sensor sensitivity, but the present invention is not limited to this. For example, the binarized signal SB may be sampled only once or continuously for a predetermined sampling period. However, the configuration of the above embodiment can be said to be a configuration in which the binarized signal SB is sampled continuously for a predetermined sampling period depending on the viewpoint. In this configuration, the sampling duration is preferably longer for fine adjustment than for coarse adjustment.

  (5) In the above embodiment, the coarse adjustment and the fine adjustment have the same unit time as the sampling interval and the number of samplings is different, but the present invention is not limited to this. The unit time may be shorter in fine adjustment than in rough adjustment. In short, it is only necessary that the accuracy for determining the adjustment value of the sensor sensitivity is different between the fine adjustment and the coarse adjustment.

(6) In the above-described embodiment, one CPU 40 performs all the printing processing and correction processing. However, the present invention is not limited to this, and a plurality of CPUs and a dedicated circuit ASIC (Application)
It may be executed by a specific integrated circuit). For example, printing during printing processing and sensitivity adjustment processing may be executed by different CPUs. Further, adjustment value determination processing and contamination / deterioration determination may be executed by different CPUs.

  1: Printer 3: Sheet 15: Mark sensor 20: Image forming unit 40: CPU 47: Drive mechanism 51: Light emitting element 52: Light receiving element M: Mark

Claims (9)

A rotationally driven carrier;
An optical sensor having a light projecting unit for irradiating light on the carrier, and a light receiving unit for receiving reflected light from the carrier;
When printing on an image forming medium, a print image is formed on the transport body or on an image forming medium transported to the transport body, and when a mark is detected by the optical sensor, a correction mark is formed on the transport body or An image forming unit formed on an image forming medium transported to the transport body;
A drive unit that performs a detection rotation for rotationally driving the transport body for the mark detection and a non-detection rotation for rotationally driving the transport body for other than the detection of the mark;
A determination unit that obtains a received light amount of reflected light received by the optical sensor during the non-detection rotation, and determines an adjustment value of the sensor sensitivity of the optical sensor from the received light amount;
An image forming apparatus comprising: a mark detection unit configured to detect the mark with sensor sensitivity after adjustment based on the adjustment value determined by the determination unit during the detection rotation. The image forming apparatus according to claim 1,
The transport body is a medium transport body that transports the image forming medium during the printing,
The non-detection rotation is a rotation drive for the printing,
The determination unit is configured to execute a transport area use process for determining the adjustment value using a received light amount of reflected light from a transport area that transported the image forming medium in the medium transport body. Forming equipment. The image forming apparatus according to claim 2,
In the determination unit, the length of the image forming medium in the transport direction of the transport body is equal to or larger than a reference length, and the width of the image forming medium in a direction orthogonal to the transport direction is equal to or larger than the reference width. An image forming apparatus that executes the transport area use process when at least one of the conditions is satisfied, and does not execute the transport area use process when the condition is not satisfied. The image forming apparatus according to claim 2, wherein:
In the transport area utilization processing, the weights received by the reflected light from the transport area are set larger than the weights by the reflected light from the non-transport area that is not the transport area, and the weighted both received light amounts An image forming apparatus, which is a process of determining the adjustment value based on The image forming apparatus according to claim 4,
The conveyance area use process is an image forming apparatus in which the adjustment value is determined only from the amount of reflected light received from the conveyance area. An image forming apparatus according to any one of claims 1 to 5,
The non-detection rotation is a rotation drive for the printing,
The image forming unit includes a plurality of image forming units that form images of different colors.
When the number of image forming units used at the time of printing is equal to or greater than a predetermined number, the determination unit does not use the amount of reflected light received by the optical sensor at the time of printing to determine the adjustment value but to use at the time of printing. When the number of image forming units is less than a specified number, an image forming apparatus that uses a received light amount of reflected light received by the optical sensor during the printing to determine the adjustment value. An image forming apparatus according to any one of claims 1 to 6,
The determination unit is configured to acquire the amount of reflected light received by the optical sensor a plurality of times or for a reference time,
When the determination unit cannot acquire all the received light amounts for the plurality of times or the reference time during the non-detection rotation, the drive unit rotationally drives the transport body for adjusting the sensor sensitivity. And the said determination part is an image forming apparatus which acquires the remaining light reception amount. An image forming apparatus according to any one of claims 1 to 7,
An image forming apparatus, comprising: a determination unit that acquires a received light amount of reflected light received by the optical sensor during the non-detection rotation and determines at least one of a contamination degree of the optical sensor and a deterioration degree of the conveyance body. A rotationally driven carrier;
An optical sensor having a light projecting unit for irradiating light on the carrier, and a light receiving unit for receiving reflected light from the carrier;
When printing on an image forming medium, a print image is formed on the transport body or on an image forming medium transported to the transport body, and when a mark is detected by the optical sensor, a correction mark is formed on the transport body or An image forming apparatus comprising: an image forming unit formed on an image forming medium transported by the transport body;
At the time of non-detection rotation for rotationally driving the carrier for other than the detection of the mark, the received light amount of the reflected light received by the optical sensor is acquired, and the sensor sensitivity adjustment value of the optical sensor is obtained from the received light amount. A decision process to decide;
A control program for executing a mark detection process for detecting the mark with sensor sensitivity after adjustment based on the adjustment value during detection rotation for rotationally driving the carrier for detecting the mark.

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